Process for transportation of waxy crude oils

ABSTRACT

An improved process for the transportation of waxy crude oils through pipelines, in particular North African crudes, which comprises introducing into the pipeline a low-pour point, lowsulfur crude oil blend comprising about 70 to about 90 percent by volume of a high-pour point, low-sulfur, waxy crude, and about 30 to about 10 percent by volume of a low-wax, low-pour crude, together with an effective pour depressant amount of an oilsoluble ethylene-vinyl fatty acid ester copolymer. The pipeline flow characteristics of the blend of the crudes are distinctly superior to the high-pour point, low-sulfur, waxy crude forming the major portion of the blend or the high-pour point, waxy crude with the same pour point depressant. In another aspect, this invention relates to the composition comprising the blended crudes together with the oil-soluble copolymer and to a process for preparing such compositions.

United States Patent Sweeney et al.

[15] 3,67%,671 51 July 11, 1972 [54] PROCESS FOR TRANSPORTATION OF WAXY CRUDE OILS [72] Inventors: William M. Sweeney, Wappingers Falls; David Lee Alexander, Fishkill, both of [73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 28, 1970 [21 Appl. No.: 102,052

Primary Examiner-Alan Cohan Attnrm'yThomas H. Whaley and Carl G. Ries ABSTRACT An improved proces for the transportation of waxy crude oils through pipelines, in particular North African crudes, which comprises introducing into the pipeline a low-pour point, lowsulfur crude oil blend comprising about 70 to about 90 percent by volume of a high-pour point, low-sulfur, waxy crude. and about 30 to about l0 percent by volume of a low-wax, low-pour crude, together with an effective pour depressant amount of an oil-soluble ethylene-vinyl fatty acid ester copolymer. The pipeline flow characteristics of the blend of the crudes are distinctly superior to the high-pour point. lowsulfur, waxy crude forming the major portion of the blend or the high-pour point, waxy crude with the same pour point depressant. In another aspect. this invention relates to the composition comprising the blended crudes together with the oil-soluble copolymer and to a process for preparing such compositions.

SCIainmNoDrawings PROCESS FOR TRANSPORTATION OF WAXY CRUDE OILS 1. Field of the Invention This invention relates to an improved process for the transportation of waxy crude oils. More particularly, this invention relates to an improved process for the transportation of waxy crude oils in which a blend of a high-pour point, low-sulfur, waxy crude and a low-wax, low-pour crude together with a quantity of an oil-soluble ethylene-vinyl fatty acid ester copolymer is introduced into the pipeline.

2. Description of the Prior Art Certain waxy, low-sulfur, high-pour crude oils are known to have poor pipeline flow characteristics and, in addition, they exhibit a tendency to gel at temperatures encountered during transportation. This tendency is particularly troublesome when a pipeline containing these crudes is shut down under low ambient temperatures. With particular reference to the Trans Alpine Pipeline which moves for the most part North African waxy crudes, the pipeline authority (TAL) have set up specifications for waxy crudes to protect against pipeline freeze-up caused by mandatory or emergency shutdowns under European winter conditions. Crudes which fail to meet TAL specifications are not allowed into the pipeline. One of the important TAL specifications is yield stress value of the crude which is a measure of the stress or amount of force required to initiate flow of a gelled waxy crude. Many waxy crudes and mixtures thereof with other crudes fail to pass the minimum requirements which tentatively are set at 100 dynes per cm.

A number of processes have been suggested in the art for dealing with such flow problems. For example, the pour point of waxy crudes has been improved by the removal of a part of the wax by solvent extraction at low temperatures, with the attendant expense of recovering the solvent, and the problem of disposing of the wax and of providing the cooling requirements which are substantial. In more recently proposed processes, wax has been removed without the use of a solvent by centrifuging a previously heated crude which has been cooled at a critically controlled and slow rate to a centrifuging temperature of around 35-55 F.

Another widely practiced process involves cutting the waxy crudes with lighter fractions of hydrocarbons. This process suffers from a number of disadvantages. such as the fact that the procedure involves the use of relatively large amounts of expensive hydrocarbon solvents to transport a relatively cheap product. Furthermore, this practice also necessarily requires that the cutting hydrocarbon solvents be available in suitable quantities which in some instances is inconvenient, and also that there be a ready market for the solvents at the other end of the pipeline.

In another method, heating equipment installed along the pipeline at frequent intervals is utilized to heat the crude and thus reduce its viscosity. Heaters employed for this purpose can be operated by withdrawing from the crudes being transported for use as fuels. As much as 5 percent of the crude may be utilized in providing the heating necessary for reducing the crude oil viscosity to a suitable value. Furthermore, most pipelines are not equipped with such heating installations. Also, there is the additional problem of contamination of the atmosphere when burning crude oils since they may be difficult to burn completely.

A principal object of this invention is to provide an improved process for the transportation of waxy hydrocarbons through pipelines such as the Trans Alpine Pipeline.

Another object of this invention is to provide a crude oil composition which is a blend of a high-pour point, low-sulfur waxy crude and a low-wax, low-pour crude together with an oil-soluble ethylene-vinyl fatty acid ester copolymer which possesses improved pipeline flow properties.

Another object of the present invention is to provide for critical blending of high-pour, waxy crude oils with low-waxy, low-pour crude oils to give large increases in pour point reduction without employing elaborate dewaxing procedures.

Another object of the present invention is to form a blend of a high-pour, waxy crude oil characterized by low sulfur content which will yield on refining a residual fuel oil having a low sulfur content so as to comply with air pollution laws.

A further object of this invention is to provide a crude oil blend which will be stable at room temperature under storage times of at least 2 weeks.

Crude oil blends of this invention comprise from about 70 to about percent by volume of a high-pour, waxy crude oil having an API gravity of about 30 to about 40; a sulfur content of between about 0.0l and about 1.0 percent by weight; a Saybolt viscosity at l00 F of about 20 to about SUS; a wax content of between about 3 and 20 percent by weight and a pour point between about 40 and about 90 F, and from about 30 to about 10 percent by volume of low-wax, low-pour, crude oil having an API gravity of about 25 to about 40; a Saybolt viscosity at 100 F of about 20 to about 100 SUS; a pour point between about -40 and about +40 F; a wax content between about 0 and 3 percent by weight and a sulfur content of between about I and about 4 percent by weight, together with an effective pour depressant amount of an oilsoluble copolymer additive. A low wax, low-pour crude oil which has given particularly good results in the blends of this invention is a crude oil known as Arabian Light" which has an AP] gravity of about 34.5, a Saybolt viscosity of about 43.5 SUS at l00 F, a pour point of about -20 F, a wax content of about 2 percent by weight and a sulfur content of [.4 to L7 percent by weight. One of the high-pour, waxy, crude oils employed in the blends of this invention which is known as Amna" crude has an API gravity of about 36.0; a Saybolt viscosity of about 69.8 SUS at 100 F; a pour point of about +70 F; a wax content of about [4.0 weight percent and a sulfur content of about 0. l5 weight percent. Mixtures of the high-pour, waxy crude oils and/or mixtures the low-wax, low-pour crude oils may be utilized in preparing the crude oil blends of this inven tion, if desired.

The pour point depressant additives suitable in the practice of the invention comprise oil-soluble ethylene-vinyl fatty acid ester copolymers in which the fatty component of the ester has a carbon content of from about 2 to about 6, the copolymers having a molecular weight of about 16,000 to about 3 1,000 determined by the Number Average Molecular Weight by the Membrane Osmometry Analytical Method, a vinyl fatty acid ester content of from about 17 to about 42 percent and a melt index of from 5 to 580. The preferred copolymers are sold under the trade name of Elvax" by the E. l. Pont du Nemours Company, the most suitable being Eivax 250 which contains 27 to 29 percent vinyl acetate, has an inherent viscosity at l00 F of 0.78 dcL/gm. in toluene; a softening point as determined by A.S.T.M. E 28 of 280 F; a cloud point in paraffin wax of F, a melt index of l2-l 8; and a molecular weight of about 23,000 to about 27,000. The material is supplied by the manufacturer for use in blends containing wax, such as coating compositions for paper milk cartons, to provide toughness, flexibility, adhesion and barrier properties--properties having nothing in common with pour point reduction in crude oil blends. The subject resin additive can be prepared by a variety of processes, such as that of U.S. Pat. No. 3,215,678 in which the free radical-initiated polymerization reaction of ethylene and a vinyl ester of a lower saturated monobasic aliphatic carboxylic acid is described.

The characterization of the various Elvax additives is given in Table 1 below:

3 l 24-26 335-465 350 24-26 l6-22 360 24-26 l.6-2.4 410 [7-19 430-580 4 60 l7-l9 2.1-2.9

in g/lO min. as determined by A.S.T.M. I328 modified.

In preparing the novel crude oil blends of this invention the two different crude oil stocks, such as the Amna crude and the Arabian Light crude, and the copolymer additive are mixed together at ambient temperature and the resulting mixture heated with continued mixing to a temperature of about 100 to about 180 F and, preferably, at 100 to 150 F to form the blend composition. The quantity of the copolymer added can be varied widely and although it is only necessary to add an effective pour depressant quantity, this amount will necessarily depend upon the physical characteristics of the crude stocks being blended, and on the temperature to which the mixture is heated. The higher this temperature the less copolymer is needed to give the desired effect. Usually, from about 0.0l to about 0. l percent by weight and, preferably, from about 0.0l to about 0. l0 percent by weight of the copolymer based on the weight of the finished blend is employed. Mixtures of the useful copolymers may be utilized, if desired.

The copolymer may be added to the crude oil stocks being blended directly as granules; in a water-glycol emulsion, such as a water-ethylene glycol emulsion, or in a hydrocarbon, such as toluene, kerosene, a Udex fraction, etc. Suitable emulsions can be prepared by dissolving the copolymer in a hydrocarbon such as kerosene, etc. and then emulsifying the hydrocarbonpolymer solution with a mixture of an alkylene glycol, such as ethylene glycol, propylene glycol, etc., water and detergent to form an oil-in-water emulsion. The resulting emulsion will exhibit a pour point and viscosity close to that of the waterglycol phase. An example of this approach is the use of a water-ethylene glycol emulsion containing about 22 percent of the copolymer. This method is especially useful if the additive is to be exposed to cool weather as a similar concentration of the copolymer in a light hydrocarbon has a pour point at or above room temperature and is quite viscous due to the thickening power of the copolymer.

The specific properties of Amna and Arabian Light crudes are set forth in Table 2 below:

It was observed in experimental work leading to the present invention that the addition of 0.030 weight percent of Elvax 250 to the Amna crude i.e., the high-pour, low-sulfur waxy crude) had no significant effect on the yield stress value and, likewise, with a blend of 80 percent by volume of the Amna crude and 20 percent by volume Arabian Light crude, only minor improvement in the yield stress value was achieved. Surprisingly, when 0.030 weight percent of Elvax 250 was added to the 80/20 blend a yield stress value of dynes was achieved. These test data are summarized in Table 3 which follows:

Measured after the blend was stored two weeks at room temperature. "The blend was made with stirring at l$0F for 2 hours.

The data in Table 3 indicate that the resulting mixtures of the Amna and the Arabian Light crudes have such excellent flow property characteristics that they will pass TAL pipelines tentative yield stress specification for crude acceptance, even after storage for two weeks at room temperature.

The effect of the blending temperature and the concentration of the Elvax 250 additive on the storage stability of Amna-Arabian Light blends is shown in Table 4.

TABLE 4 Effect of Blending Temperature and Additive Concentration on Storage Stability of Amna-Arabian Light Blends Weeks to Failure Amna/Arabian Light Blend Blending Temperature, "F

% Elvax 250 in 30/20 Blend [20 170 3% Elvax 250 in JO/l0 Blend 0.0l7 0.033 0.050 0.067 Elvax 250 in 100% Amna Samples of each blend were stored at room temperature. Portions of each sample at weekly intervals were cooled to 32-35F overnight. If the sample solidified, the sample failed.

As the data in Table 4 indicate, the use of increased amounts of the additive as well as higher blending temperatures yields blends with longer, satisfactory storage times.

What is claimed is:

I. In the transportation of waxy crude oils by pipeline, the improvement which comprises introducing into the said pipeline a low-pour point, low-sulfur crude oil blend comprising about 70 to about percent by volume of a high-pour, waxy crude oil having a pour point of between about 40 and 90 F and about 30 to about 10 percent by volume of a lowwaxy, low-pour crude oil together with an effective pour depressant amount of oil-soluble ethylene-vinyl fatty acid ester copolymer in which the fatty acid component of the ester has a carbon content of from about 2 to 6, said copolymer having a molecular weight of between 16,000 and 3 I ,000', a melt index of about 5 to about 580 and a vinyl fatty acid ester content of from about 17 to about 42 percent by weight.

2. The method of claim 1 wherein the said high-pour, waxy crude oil has an AP] gravity ranging between about 30 and about 40; a sulfur content between about 0.0l and about 1.0 percent by weight; a Saybolt viscosity at F of about 20 to about l00 SUS; and a wax content of between about 3 and 20 percent by weight.

3. The method of claim 1 wherein the said low-waxy, lowpour crude oil has an AP! gravity of about 25 to about 40; a Saybolt viscosity at I F of about 20 to about 100 SUS; a pour point of about -40 to about +40 F a wax content of about 1 to about 4 percent by weight and a sulfur content of between 0 and about 3 percent by weight.

4. The method of claim 1 wherein the amount of the said copolymer in the said blend is from about 0.01 to about 0.15 percent by weight based on the weight of the blend.

5. The method of claim 1 wherein the said vinyl ester is vinyl acetate.

6. The method of claim 1 wherein the said crude oil blend contains about 80 percent by volume of the high-pour, waxy crude oil and about 20 percent by volume of the low-waxy, low-pour crude oil together with from about 0.01 to about 0. l 5 percent by weight, based on the total weight of the blend, of the said copolymer.

7. The method of claim 1 wherein the said blend comprises a mixture of the said high-pour. waxy crude oils and a mixture new of the said low-waxy, low-pour crude oils.

8. The method of claim I wherein the said low-pour point, low-sulfur crude oil blend comprises about percent by volume of a high-pour crude oil having an API gravity of about 36; a sulfur content of about 0. l5 percent by weight; a Saybolt viscosity at F of about 69.8 SUS; a wax content of about 14 percent by weight and a pour point of about +70 F and about 20 percent by volume of a low-waxy, low-pour crude oil having an AP! gravity of about 34.5; a Saybolt viscosity at 100 F of about 43.5 SUS', a pour point of about 20 F; a wax content of about 2.0 percent by weight, and a sulfur content between about 1.4 and about 1.7 percent by weight. together with about 0.0] to about 0. 15 percent by weight, based on the weight of the total blend. of an ethylene-vinyl acetate copolymer having a molecular weight of about 23,000 to about 27,000, a vinyl acetate content of about 27 to 29 percent by weight and a melt index of 12-18.

i t i i \I 

2. The method of claim 1 wherein the said high-pour, waxy crude oil has an API gravity ranging between about 30 and about 40; a sulfur content between about 0.01 and about 1.0 percent by weight; a Saybolt viscosity at 100* F of about 20 to about 100 SUS; and a wax content of between about 3 and 20 percent by weight.
 3. The method of claim 1 wherein the said low-waxy, low-pour crude oil has an API gravity of about 25 to about 40; a Saybolt viscosity at 100* F of about 20 to about 100 SUS; a pour point of about -40* to about +40* F; a wax content of about 1 to about 4 percent by weight and a sulfur content of between 0 and about 3 percent by weight.
 4. The method of claim 1 wherein the amount of the said copolymer in the said blend is from about 0.01 to about 0.15 percent by weight based on the weight of the blend.
 5. The method of claim 1 wherein the said vinyl ester is vinyl acetate.
 6. The method of claim 1 wherein the said crude oil blend contains about 80 percent by volume of the high-pour, waxy crude oil and about 20 percent by volume of the low-waxy, low-pour crude oil together with from about 0.01 to about 0.15 percent by weight, based on the total weight of the blend, of the said copolymer.
 7. The method of claim 1 wherein the said blend comprises a mixture of the said high-pour, waxy crude oils and a mixture of the said low-waxy, low-pour crude oils.
 8. The method of claim 1 wherein the said low-pour point, low-sulfur crude oil blend comprises about 80 percent by volume of a high-pour crude oil having an API gravity of about 36; a sulfur content of about 0.15 percent by weight; a Saybolt viscosity at 100* F of about 69.8 SUS; a wax content of about 14 percent by weight and a pour point of about +70* F and about 20 percent by volume of a low-waxy, low-pour crude oil having an API gravity of about 34.5; a Saybolt viscosity at 100* F of about 43.5 SUS; a pour point of about -20* F; a wax content of about 2.0 percent by weight, and a sulfur content between about 1.4 and about 1.7 percent by weight, together with about 0.01 to about 0.15 percent by weight, based on the weight of the total blend, of an ethylene-vinyl acetate copolymer having a molecular weight of about 23,000 to about 27,000, a vinyl acetate content of about 27 to 29 percent by weight and a mElt index of 12-18. 